1. Field of the Invention
The invention deals with optical devices and can be used in designing the equipment for light beam shaping and spatial restructuring, and more particularly, to a micro lens array designed to make use of the total internal reflection and intended for wide-angle lighting systems.
2. Description of the Related Art
The micro lens array for transformation of light beams is generally used as a structured screen to control propagation (pass) or diffusion of an incident light beam. The micro lens array is a set of micro lenses with sizes from 10 up to 200 micrometers which are packed by one of known methods, for example, by means of the rectangular or hexagonal packing, on one surface.
Existing micro lens arrays enable increasing an angle of divergence of an incident beam up to 110-120 degrees, with efficiency of such devices ranging from 50% to 80%. However there are cases (for example, back light for TFT displays) where such angles of divergence are insufficient and the angle of divergence of radiation must be at least 130 degrees. Such angle of divergence can be gained either by application of materials with higher refractive index or by application of basically new optical solutions.
Various kinds of materials are used for the micro lens array production, and the most common is a transparent polymethyl methacrylate. The refractive index of this material is 1.49. This value imposes certain restrictions on the maximum angle of divergence and does not allow gaining angles over 110 to 120 degrees. At such angles the array efficiency does not exceed 80%. This phenomenon is a result of refraction of the part of Fresnel loss or structural limitations of the inner surface (the inside) of the array at greater angles.
Let's consider some known solutions based on the micro structured optics.
US patent publication No. 2002/0034710 discloses the methods are described for forming the structured screens for transformation of an input beam to a beam with controlled parameters. The structured screen is a set of the micro lenses located on a surface, and parameters of each micro lens are governed by a certain law. Such screen transforms an input beam into a divergent beam with determined parameters. The drawback of the said patent consists in limited angle of divergence of the output beam, which is a result of the insufficient refractive index of the used material.
U.S. Pat. No. 6,456,437 discloses the most similar to the claimed solutions. The authors offer to use a disordered array of prisms located on one surface, to solve a problem of magnification of the divergence angle and of homogenization of an incoming light beam. The angles of prisms are chosen in such a way that the incoming beam undergoes total internal reflection. The drawback of the said method consists in difficulty of obtaining uniform light distribution or a specific angle of divergence due to the limited conditions of the incoming radiation or angles of prisms.